Spray drying starch conversion syrup



Patented Dec. 30, 1947 ,IUNITED STAT srnnr DRYING STABCH CONVERSION snwrHerman H. Schopmeyer, Hammond, Ind., assignor to American Maize-Productscorporation ofMaine No Drawing. Application March 20, 1945,

Serial No. 583,859

This invention relates to spray drying starch conversion syrup.

Considerable success has been realized in recent years in drying cornsyrup in finely atomized condition, to give a highly desirable form ofsyrup solids. These solids may be shipped in bags, not only saving onthe cost of the containers over the cost of cans or drums ordinarilyused for syrup but also reducing freight charges uponthe water contentof usual corn syrup. In addition the syrup solids have been found tohave advantages in certain'arts over the original syrup fro which thesolids are made. 7

In spite of. these advantages, the production of the spray dried syrupsolids has beenlimited.

"3 Claims. (01.127 34) The chief reason for the limitation is thecostliness of the equipment and the expense of operation per ton ofproduct, 7 r

The equipment that'has been in useincludes a large cylinder which isordinarily 20 ft. or so in diameter with a conical bottom, theshapebeing generally that of a large cyclonic collector such ,as is in commonuse for separating suspended the droplets during the drying operation,carefulcontrol being necessary with corn syrup especially .because ofthe known fact'that the solids of corn syrup are subject todiscoloration and the development of off-flavored material if local overheating is permitted or a given droplet, in the spray is exposed for toolong a time to the temperature of drying. I

In this operation as performed heretofore, the syrup to be sprayed ispreheated to about as high a temperature as permissible withoutdeveloping off-color or objectionable flavor and the air delivered tothe drying chamber or cyclone is also preheated. In order to reduce thetemperature gradient as much as possible and thus prevent a scorching,the temperature to whichthe air is ordinarily preheated in drying thecorn syrup in commercial operations has been kept at a temperature ofabout 320 F. or below and the size of the atomized droplets ofsyrup'kept very small, the smallness of size minimizing the differenceof temperature between the inside and outside of the droplets duringheating, so as to avoid scorch- Company, a

ing the exterior-while at the same time causing drying of the interior.

I have now discovered a method of increasing by three to five times thecapacity of commercial spray drying units for corn syrup or like starchconversion syrup. This increase of capacity has been attained bydiscarding and proceeding contrary to the previously acceptedpractices'which were considered necessary with the heat-'decome posablesolids of the. syrup.

Briefly stated, the invention comprises preheating starch conversionsyrup, spraying the preheated syrup in the form of coarse droplets, ofaverage diameter about to 40 microns, into a stream of moving airpreheated to an abnormally high temperatureof about 400 to 520 F., andseparating the, resulting dried particles of the'syrup solids from theair at a moisture content of the solids of at least approximately 1. percent. In the preferred embodiment, the invention comprises the use ofsomewhat more restricted conditions which givev particularly desirableresults, namely, making thev average dimeter of the droplets to microns,preheating the mass of air to 440 to 490, and separating the resultingdriedparticles of syrup solids when the moisture content has beenreduced .to approximately 0.5% to 4%.- In one embodiment the inventioncomprises spraying the preheated syrup at-a density of to B. andpreferably at about42 to 44 B. I

It will be noted that .two conditions have been changed which should beexpected to make for a greater difference of temperature'between theoutside and the inside of the droplets of corn syrup and thus increasethe danger of overheating of the exterior of the droplets.

First, the droplets have been mademuch larger than those heretoforeused. Since the volume of a sphere varies with the cube of the diameter,the droplets which I use are many times greater in weight than .thesmaller droplets referred to. Thus a droplet of 15 microns diameter hasa volume and therefore weight that is 6 hr 216 times as great asdroplets of diameter 2.5 microns.

In the second place, the temperature of drying has been made much higherthan that heretofore considered necessary, this again seeeminglyincreasing the likelihood of local overheating and scorching of thesolids of the exterior portions of the relatively large droplets to acertainty.

I have found, however, that the operation may be conducted smoothly andsuccessfully under the extreme conditions recited. Instead of the twochanges in conditions contributing each to the overheating or scorchingor the exterior, I have found thatthe largcr droplets are able towithstand higher air temperatures, presumably because the wet coreprotects them until the temperature of the drying air is greatlyreduced.

Thus it is possible to work. with air admitted to the cyclonic chamberat temperatures as high as 490 to 520 F. with the product of. driedmaterial of satisfactory flavor and color, whereas, with the smaller andpresumably more uniformly heated droplets, temperatures substantiallyabove 320 F. in the inlet air are to be avoided.

In general, the equipment used in my improved process is conventionalexcept for changes of a simple mechanical nature in the spraying mech.anism. These changes involve increase in the size of openings throughwhich the syrup is forced in the spraying process and suitably alsoincrease in the speed of the centrifugal spinner which is provided withthese openings and which atomizes the syrup. The size of the openingsand speed of rotation required to give the coarse droplets are easilydetermined by a few simple experiments with any given syrup beingsprayed. Thus, I have used to advantage a conventional type of spraymechanism with fans, the atomizer proper consisting essentially of abasket type centrifuge of diameter 14 inches with vertical slots in theouter wall thereof, the slots being spaced apart laterally by V inch oncenters and each slot A; inch wide and V inch long, and the basket beingrotated at a speed of 14,500 R. P. M. A fan within the mechanism assistsindelivering the,

syrup through the slots and a second fan promotes quick removal of thesyrup from the outside of the basket and suspension in a rapidly movingstream of air, all in accordance with mechanism heretofore known exceptfor the stated modification of size of slots and speed of rotation.

The starch conversion syrup to be used may be usual corn syrup such assocalled corn syrup unmixed (C. S. U.) or a like material made byconversion of potato, wheat, rice or like starch.

The temperature of preheating of the syrup before spraying may be andpreferably is much higher than that previously used in this art, as, forinstance, 220 to 280 F., and preferably 240 to 260 F.

This higher temperature of heating by reducing the viscosityof the syrupmakes possible spraying more concentrated syrups and thus reduces theevaporation load on the spray drier.

Thus, I may use corn syrups of water content as 50 5 such quantity thatthe suspended air which is separated from the dried syrup solids at thebottom of the cyclone issues from the cyclone at a temperature around160 to 200 F., the syrup solids themselves are dried to a moisturecontent of /2 to 4% and their temperature is about 110 to 130 F. at thetime of the separation.

Plant scale data, on a. typical run using the corn syrup unmixed (C. S.U.) and spray drying it as large droplets predominantly'of size to 40 15microns, are given below:

n F... 230 Density of C. S. U. feed, 315. ....degrees 43 Intake airtemperature of spray dryer Outlet air temperature from spray dryer-- 186Temperature of discharge of product- F... 119 Color of product .86Moisture content of product per cent 1.0

Volume of intake air for C. S. U. equivalent to 2,950 lbs. of productper hour cu. ft./min 7,500

C. SLU. feed (temperature. of preheat- In spite of the high temperatureof the air usual type and in spite of the large droplets,showing'necessarily an abnormally large difference of temperaturebetween the outside and inside of the droplets, the product was ofexcellent quality. It was granular and free flowing and entirelysatisfactory in color and flavor.

It will be understood that. it is intended to cover all changes andmodifications of the example of the invention herein chosen for thepurpose of illustration which does not constitute departures from thespirit and scope of the invention.

What I claim is: 1. The method of spray drying starch conver- 45 sionsyrup which comprises preheating the syrup, spraying the preheatedsyrup, at a temperature low as 19% or slightly less as against 35% whichwas formerly about the minimum in this operation. In general, I may highas Be. as compared to syrup of density 37 B. that has been foundheretofore to work best when the atomization and the temperature of theinlet air were controlled in accordance with. the practice understood tobe necessary.

My method of operation is that which is conventional except as specifiedherein. to be otherwise. The preheated syrup is sprayed into the mass ofheated air, the syrup being sprayed in use syrup of density as the formof droplets of averag diameter 15 to 40 microns and preferably 20 to 30microns. This 65 means that the maior part of the mass of the to B. andpreferably 43 to 44 syrup is in the form of droplets of the range ofdiameters stated and that droplets of smaller diameter constitute atmost only a minor part by weight of the total mass of the syrup sprayed.

The syrup is sprayed into the preheated mass of air moving through thedrier chamber. As the heat of the air is utilized in evaporating waterfrom the droplets, the temperature of the air falls. The air must beused in quantity ade- Name Date 1,670,101 Dickerson May 15, 19282,192,951 Wolfl Mar. 12, 1940 2,324,113 Schopmeyer July 13,19432,317,479 Peebles et a1. Apr. 27, 1943 of aboutv 220 to 280 F. and inthe form of droplets averaging 15 to 40 microns in diametenintd a movingmass of air preheated to a temperature between 400 and 520 F., andseparating the resulting particles of dried syrup solids from the air ata moisture content of the solids of at least approximately 0.5-per cent.1

2. The method described in claim 1, the syrup I 55 being sprayed at aconcentration corresponding to:

a density of 40 to 45 B15. and the preheated air being-used inproportion to dry the syrup solids to a moisture content of 0.5% to 4%as the temperature of the air falls about 250 F. during the drying.

3. The method described in claim 1, the temperature of the preheatedair-being 440 to 480 F. HERMAN H. SCHOPMEYER.

rtnrnanncns crrnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS I Number at the intake to the cyclonic dryingchamber of

